While I don't know for certain, I haven't uploaded a game to this site yet, I have spoken with other developers and I recall hearing about something called "Butler" which is needed for the itch app to receive the download option. You'd want to do some googling yourself since I'm not positive, but I hope that helps get this to work on the itch app!
Edit: Checked your profile and noticed you're reuploading the game for each update, you'll want to be updating the same game if you do this, that way people can just redownload and transfer saves much easier. It'll also notify itch app users of updates and allow them to install them when they're released. Hope this helps!